Inhibitor and the use thereof



Patented Oct. 11, 1932 UNITED STATES" PATENT oluucs .AND COMPANY, OF SYLVANIA No Drawing.

My invention relates to a chemical compound to be used in conjunction with pickling solutions, and more particularly it re-. lates to a new inhibitor which will prevent the sulphuric or other acid substance of the pickling solution from attacking the surface of the iron or steel being treated.

The principal object of my invention is to provide a picklin solution which will most effectively and e lciently remove the scale and rust from iron and steel surfaces without pitting or corroding to any measurable extent the surface of the object being treated.

Still another object of my invention is to provide a solution of S111 huric or other acid which will be re a We y inert towards the ferrous metals, and, therefore, can be shipped in iron or steel containers without danger of appreciable corrosion thereof.

Other objects, including the novel method of pickling, will appear from aconsideration of the specification and claims.

In the fabrication of metals, or metal objects, the surfaces thereof become oxidized to some extent, particularly after the various metallurgical processes involving the heating of the metal. This oxidation of the surface results in the formation of a certain amount of iron or other oxides, known in the trade as scale or rust. This scale or rust JOSEPH M. LEAPER, OP PHILADELPHIA, PENNSYLVANIA, ASSIGNOR T0 E. F. HOUGHTON PHILADELPHIA, PENNSYLVANIA, A CORPORATION OF PENN- INHIBI'IOR AND THE USE THEREOF Application filed May 9, 1931. Serial No. 536,317.

where the scale has been removed, the surface of the metal is attacked b the acid:

. The addition to the pickling solution of various organic substances has from time to time been suggested, such substances being added to the pickling acid for the purpose of lessening the action of the acid on the surface of the iron or steel. The usefulness of these inhibitors depends to a large extent on their efficiency, that is to say, it depends on the amount of inhibitor needed for each pound of acid consumed in the pickling operation. The substances suggested for use in connection with the pickling solutions have been of a wide variety of materials, some of them, for example, consisting of the crude products of various pyridine distillates from coal tar, while others are more clearly defined chemically such as diorthotolylthiourea. The inhibitor of the present invention has been found to be more eflicient than any of the inhibitors hitherto proposed for use.

My invention contemplates the use as inhibitors of the class of compounds known as aldehyde merca-ptals whose formula may be represented as follows:

is removedhythesoscalled pickling processes Where 1 and 2 may be the same or diiferent in, which w l I d I 1 tacking 'jcl'oln'pounds, sup 1 as 1 roc oric acid or a bisulphite, are employed. The disadvantage in the use of scale-removing compounds resides in the fact that after the acid has attacked and removed the scale, it continues to act, with the result that the surface of the metal itself is pitted and corroded.

This action on the surface of .the metal is accompanied by the evolution of disagreeable gases. In commercial practice, it is not pos- Y sible to remove the scale or rust without also attacking the metal, since there is no indication when the process should be stopped.

Furthermore, the rust and scale do not cover the metal surface uniformly, and, therefore,-

- the acid dissolves the scale atone point onthe surface, while at some adjacent point.

sulphurje acid or otligrscmalkyl, unsubstituted aryl, or aralkyl groups and B, may be hydrogen or any alkyl, unsubstituted aryl, or aralkyl group. The unsubstituted groups contemplated are the alkyl,

aralkyl, and aryl in which the-re has been no substitution of the hydrogen of the group by sulphur, chlorine, or like elements.

These compounds are prepared by condcnsing one molecule of an aldehyde with two mercaptan molecules. Thus, if two molecules of a single mercaptan are reacted with aromatic aldehyde, or an aralkyl aldehyde is reacted with two molecules of the mercaptan,

then R. will be the corresponding alkyl, aryl,

or aralkyl group. The condensation reac- 5 tion results from the splitting off of water during the progress of the reaction, the oxygen for its formation coming from the aldehyde; while each of the mercaptan molecules furnish one hydrogen atom for its formation.

It will thus be seen that the choice of the particular mercaptal for use as a pickling inhibitor will be largely dependent upon the .availability of the compounds employed in the formation of the mercaptal. Any one of the aldehyde mercaptals are applicable for use, but in a typical case the dibenzyl formaldehyde mercaptal will be considered.

This compound may be prepared as de- 23 scribed by Fromm, Forster and Scherschewitski in Annalen, volume 394, pages 343 to 349.

As described there, the dibenzyl formaldehyde mercaptal is obtained by saturating a mixture of benzyl mercaptan and formalde- 25 hyde with hydrochloric acid gas. The benzyl mercaptan and formaldehyde are used in proportions of two molecules of the former to one molecule of the latter. The resulting compound may then be purified. In its use 33 as an inhibitor, however, it is not necessary to use a purecompound unless it is desired, as the crude substance resulting from the above reaction, or from. any other reaction in which the main product is dibenzyl formaldecli hyde mercaptal is suitable for use as a pickling inhibitor. Analogous processes may be employed in the manufacture of the other aldehyde mercaptals. For example, if diethyl acetaldehyde mercaptal is desired, it ca may be prepared by condensing ethyl mercaptan with acetaldehyde in the ratio of two molecules of the mercaptan with one molecule of the aldehyde. If a mixed mercaptal is desired, for example, ethyl benzyl formal- .5 dehyde mercaptal, it may be obtained by reacting one molecule of ethyl mercaptan and one molecule of benzyl mercaptan with one molecule of formaldehyde. The compound for use as an-inhibitor may also be made b refluxing a solution of an organic thiosu phate, such as sodium benzyl thiosulphate,

with the aldehyde. p

The mercaptal, either crude or ure, may be employed in the pickling bath by dissolving it in strong sulphuric acid and adding the solution thus obtained to water to form the pickling bath, the amount of a qi d' and water used dependingfion tlie strength of the solutifi'iequiredfor' th''pickling ofii'ation. so his solution generally contains about ten per cent by weight of sulphuric acid. In the case of the benzyl formaldehyde mercaptal, it may be employed in a proportion of one part of the compound to two thousand parts of the 05 solution, which solution contains about ten per cent by weight of sulphuric acid. A pickling solution of this composition gives excellent results, and very little, if any, loss in weight of the metal occurs. For example, in pickling Bessemer tin plate at 200 degrees F., or even higher, a weight loss of less than onequarter of one per cent results. The other aldehyde mercaptals may be used in the same percentage as that given for dibenzyl formaldehyde mercaptal. Since, however, no 7 difliculty is encountered if larger amounts are employed, the percentage given is not to be considered limiting.

Instead of dissolving the aldehyde mercaptal in strong sulphuric acid as described, it 89 may be mixed with any suitable diluting agent, such as is customarily. employed in compounding commercially marketed inhibitors, and various agents may be added if desired for the purpose of producing foam on the pickling bath, or for any other purpose in accordance with standard practices. The inhibitor of the present invention is also effective when emplo ed with other pickling acids or solutions 0 compounds resulting in acid, such as hydrochloric acid or sodium bisulphite. The inhibitor may be used in amounts in general corresponding to those hereinbeforegiven in the specific example, although the amounts may be materially increased thereover, if desired. In the claims, the term pickling acid is used to include these compounds as well as sulphuric acid.

Considerable modification 1s possible in the choice of the particular aldehyde mer- 1 captal employed, as well as the proportion thereof used in the picklin solution without departing from the essential features of my Invention.

.-I claim: 133

1. The process of pickling iron and steel which comprises subjecting said material to the action of a relatively dilute pickling acid solution to which has been added a small quantity of a. compound selected from that group of compounds whose formula is 110 where R and R are the same or different unsubstituted alkyl, aryl, or aralkyl groups,

n I R1.S.(5.S.Rl

I where R and R are the same or different 3 i quantity of :1. formaldehyde mercaptal.

unsubstituted alkyl groups, and where R, is hydrogen, or an unsubstituted alkyl, aryl, or an aralkyl group.

3. The process of pickling iron and steel 5 which comprises sub ectin said material to h the action of a relatively dllute pickling acid solution to which has been added a small quantity of a compound selected from that group of compounds whose formula is R|.B.$.8.Rg

where R and R are the same or different unsubstituted alkyl aryl, or aralkyl groups.

5. The process of which comprises 'subjectin said material to i the action of a relatively dilute pickling acid 30 solution to which has been added a small quantity of a compound selected from that group of compounds whose formula is where R; and R, are the same or different unsubstituted alkyl groups. 6. The process of pickling iron and steel which comprises sub ectin said material to the action of'a relatively dllute ickling acid solution to which has been a ded a small quantity of a com ound selected from'that group of compoun s whose formula is R .S.CH .S.R,

where R and R are'the same or different aryl groups.

7. The process of ickling iron and steel which comprises sub ecting said material to the action of a relatively dilute sulphuric 'acid solution to which has been added a small quantity of an aldehyde mercaptal.

8. The process of pickling iron and steel which comprises sub ecting said material to the action of 'a relatively dilutesulphuric acid solution to which has been added a small 9. The process of pickling iron and steel which comprises sub ecting said material to the action of a relatively dllute pickling acid solution'to which has been added a, small 'qulantity of dibenzyl formaldehyde mercapta 0 I I i 10. The process of pickling iron and steel I which comprises subjecting said material to 05 the action of a relatively dilute sulphuric pickling iron and steel acid solution to which has been added asmall quantity of dibenzyl formaldehyde mercaptal.

11. A pickling bath for removing scale and rust from iron -and steel comprising a relatively dilute pickling acid solutlon and a small quantity of a compound selected from that group of compounds whose formula is H RLSALSJI:

where R and R are the same or different unsubstituted alkyl, aryl, or aralkyl groups, and where R is hydrogen or an unsubstituted alkyl, aryl, or an arakyl group.

12. A pickling bath for removing scale and rust from iron and steel comprlsing a relatively dilute ickling acid solution and a small quantity of a compound selected from that group of compounds whose formula is g E R1. S .33. 8.1!:

where R and R are the same or difierent unsubstituted alkyl groups, and where R, is

hydrogen or an unsubstituted alkyl, aryl, or an aralkyl group.

13. A pickling bath for removing scale and rust from iron and steel comprlsing arelatively dilute pickling acid solution and a small quantity of a compound selected from i that group of compounds whose formula is H B aden,

where R and R are the same or difl'erent aryl groups, and where R, is hydrogen or an alkyl, aryl or aralkyl group.

' pickling bath for removing scale, and rust from iron and steel comprising a relatively dilute pickling acid solution and a small quantity of a compound selected from that group of compounds whose formula is R1.S.GH;.S.R= J where R and R are the same or difierent' unsubstituted alkyl, aryl, or aralkyl groups.

scale I 15. A pickling bath for removing and rust from iron and, steel comprising a relatively dilute pickling, acid solution and a small quantity of a compound selected from that group of compounds whose formula is R .S.CH,.S.R,

where R and R are the same or different unsubstituted alkyl groups.

16. A pickling bath for removing scale and rust from iron and steel comprising a relatively dilute pickling acid solution and a small quantit of a compound selected from that group 0 compounds whose formula is R .S.CH .S.R

where R and R are the same or different aryl groups.

17. A pickling bath for removing scale and rust from iron and steel comprising'a relatively dilute sulphuric acid solution and a small quantity of an aldehyde mercaptal.

18. A pickling bath for removing scale and rust from iron and steel comprising a relatively dilute sulphuric acid-solution and a imall quantity of a formaldehyde mercapta 19. A pickling bathfor removing scale and rust from iron and steel comprising a relatively dilute picklin acid solution and a small quantity of ibenzyl formaldehyde mercaptal.

20. A pickling bath for removing scale and rust from iron and steel comprising a relatively dilute sulphuric acid solution and a small quantity of dibenzyl formaldehyde mercaptal.

JOSEPH M. LEAPER. 

